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添加应用内导航</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="tutorial/toh-pt6" title="第六部分：通过 HTTP 来获取并保存英雄数据。" target="_self"><span>6. 从服务器获取数据</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="通过数据绑定构建动态视图" aria-pressed="false"><span>组件与模板</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a 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调用指令和组件的生命周期钩子函数，包括它的创建、变更和销毁时。" target="_self"><span>生命周期钩子</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/component-interaction" title="在不同的指令和组件之间共享信息" target="_self"><span>组件交互</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/component-styles" title="添加专属于某个组件的样式" target="_self"><span>组件样式</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dynamic-component-loader" title="动态加载组件" target="_self"><span>动态组件</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/elements" title="把组件转换成自定义元素" target="_self"><span>Angular 元素</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/attribute-directives" title="属性型指令把行为添加到现有元素上。" target="_self"><span>属性型指令</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/structural-directives" title="结构型指令可以操纵页面的布局" target="_self"><span>结构型指令</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/pipes" title="管道可以在模板中转换显示的内容。" target="_self"><span>管道</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 的表单" aria-pressed="false"><span>表单</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/forms-overview" title="表单可以创建集中、高效、引人注目的输入体验。Angular 表单可以协调一组数据绑定控件，跟踪变更，验证输入，并表达错误信息。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/reactive-forms" title="使用 FormBuilder、表单组和表单数组创建响应式表单。" target="_self"><span>响应式表单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/forms" title="使用指令和 Angular 模板语法创建模板驱动表单。" target="_self"><span>模板驱动表单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/form-validation" title="验证用户的表单输入" target="_self"><span>表单验证</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dynamic-form" title="使用 FormGroup 渲染动态表单。" target="_self"><span>动态表单</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Observable 与 RxJS" aria-pressed="false"><span>Observable 与 RxJS</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/observables" title="" target="_self"><span>可观察对象(Observable)</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/rx-library" title="" target="_self"><span>RxJS 库</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/observables-in-angular" title="" target="_self"><span>Angular 中的可观察对象</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/practical-observable-usage" title="" target="_self"><span>用法实战</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/comparing-observables" title="" target="_self"><span>与其它技术的比较</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 中的模块" aria-pressed="false"><span>NgModules</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodules" title="使用 NgModule 让你的应用更高效" target="_self"><span>NgModule 简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-vs-jsmodule" title="JavaScript 模块和 NgModule 之间的差异" target="_self"><span>JS 模块 vs NgModule</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/bootstrapping" title="告诉 Angular 如何在根 &quot;AppModule&quot; 中构造和引导应用。" target="_self"><span>应用的根模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/frequent-ngmodules" title="介绍最常用的 NgModule" target="_self"><span>常用模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/module-types" title="介绍特性模块的几种类型" target="_self"><span>特性模块的分类</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/entry-components" title="关于 Angular 中入口组件的一切" target="_self"><span>入口组件</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/feature-modules" title="创建特性模块，以组织你的代码" target="_self"><span>特性模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/providers" title="服务提供商与 NgModule" target="_self"><span>服务提供商</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/singleton-services" title="创建单例服务" target="_self"><span>单例服务</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/lazy-loading-ngmodules" title="惰性加载模块，以提高应用的性能" target="_self"><span>惰性加载的特性模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/sharing-ngmodules" title="共享 NgModule 让你的应用现代化。" target="_self"><span>共享 NgModule</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-api" title="理解 NgModule 的那些细节。" target="_self"><span>NgModule API</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-faq" title="回答关于 NgModules 的常见问题。" target="_self"><span>NgModule 常见问题</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="依赖注入：创建并注入各种服务。" aria-pressed="false"><span>依赖注入</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection" title="Angular 的依赖注入系统能够为 Angular 创建的类创建并交付它们所依赖的服务。" target="_self"><span>Angular 依赖注入</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/hierarchical-dependency-injection" title="与组件树平行的注入器树，并支持嵌套的依赖。" target="_self"><span>多级注入器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-providers" title="各种提供商类型的更多知识。" target="_self"><span>DI 提供商</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-in-action" title="依赖注入的使用技巧" target="_self"><span>DI 实战</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-navtree" title="使用注入器树来查找父组件。" target="_self"><span>浏览组件树</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/http" title="通过 HTTP 协议与远程服务器对话。" target="_self"><span>HttpClient</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/router" title="揭示如何通过 Angular 路由进行基本的屏幕导航。" target="_self"><span>路由与导航</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 动画系统指南" aria-pressed="false"><span>动画</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/animations" title="Angular 动画的基础技术。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/transition-and-triggers" title="转场与触发器的高级技术。" target="_self"><span>转场与触发器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/complex-animation-sequences" title="复杂的 Angular 动画序列。" target="_self"><span>复杂序列</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/reusable-animations" title="创建可复用的动画。" target="_self"><span>可复用动画</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/route-animations" title="为路由提供转场动画。" target="_self"><span>路由转场动画</span></a></div></aio-nav-item></div></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="把 Angular 用到你的实际工作中的一些技巧" aria-pressed="false"><span>其它技术</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/security" title="Angular 应用开发中的安全技术。" target="_self"><span>安全</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/i18n" title="把应用模板中的文本翻译成多种语言。" target="_self"><span>国际化（i18n）</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/accessibility" title="设计能被所有用户访问的应用" target="_self"><span>无障碍（a11y）</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular Service Worker: 控制应用资源的缓存。" aria-pressed="false"><span>Service Worker 与 PWA</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-intro" title="Angular 对 Service Worker 的实现提升了慢速或不稳定的网络连接下的用户体验。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-getting-started" title="在 CLI 项目中启用 Service Worker，并在浏览器中查看效果。" target="_self"><span>快速上手</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/app-shell" title="在 CLI 项目中启用应用外壳。" target="_self"><span>应用外壳</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-communications" title="那些能让你和 Angular 的 Service Worker 通讯的服务类。" target="_self"><span>与 Service Worker 通讯</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-devops" title="使用 Service Worker 运行应用、管理应用更新、调试以及杀掉正在运行的应用。" target="_self"><span>生产环境下的 Service Worker</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-config" title="配置 Service Worker 的缓存行为。" target="_self"><span>Service Worker 配置</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/universal" title="使用 Angular Universal 在服务端渲染 HTML。" target="_self"><span>服务端渲染</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="把 AngularJS 应用增量式的升级到 Angular。" aria-pressed="false"><span>从 AngularJS 升级</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/upgrade" title="把 AngularJS 应用增量式的升级到 Angular。" target="_self"><span>升级步骤</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/upgrade-performance" title="用更灵活的方式把 AngularJS 升级到 Angular。" target="_self"><span>更关注性能的升级方式</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ajs-quick-reference" title="学习如何把 AngularJS 的概念映射到 Angular 中。" target="_self"><span>AngularJS 与 Angular 的概念对照</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="使用共享库扩展 Angular" aria-pressed="false"><span>开发 Angular 库</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/libraries" title="理解何时以及如何使用和创建库。" target="_self"><span>库概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/using-libraries" title="把已发布的库集成进你的应用中。" target="_self"><span>使用已发布的库</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/creating-libraries" title="通过创建、发布和使用你自己的库来扩展 Angular。" target="_self"><span>创建库</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="理解原理图" aria-pressed="false"><span>原理图（Schematic）</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics" title="理解 Angular 如何使用原理图。" target="_self"><span>原理图概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics-authoring" title="理解原理图的结构。" target="_self"><span>制作原理图</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics-for-libraries" title="使用原理图来把你的库集成进 Angular CLI 中。" target="_self"><span>库的原理图</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/cli-builder" title="使用构建器定制 Angular CLI。" target="_self"><span>CLI 构建器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/web-worker" title="在 Angular CLI 中使用 Web Worker。" target="_self"><span>Web Worker</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="关于构建、测试和部署的信息" aria-pressed="false"><span>开发工作流</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="理解 AOT 预先编译器。" aria-pressed="false"><span>AOT 预先编译器</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/aot-compiler" title="学习为何以及如何使用预先编译器。" target="_self"><span>预先编译</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/angular-compiler-options" title="配置 AOT 编译。" target="_self"><span>Angular 编译器选项</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/aot-metadata-errors" title="解决 AOT 编译错误。" target="_self"><span>AOT 元数据错误</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/template-typecheck" title="Angular 中的模板类型检查。" target="_self"><span>模板类型检查</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/build" title="构建应用及为应用启动开发服务器。" target="_self"><span>构建与运行</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/bazel" title="如何配置你的环境，以利用 Bazel 进行构建和测试。" target="_self"><span>使用 Bazel 进行构建</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/testing" title="测试 Angular 应用的技巧与实践。" target="_self"><span>测试</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/deployment" title="了解如何部署 Angular 应用。" target="_self"><span>发布</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="与开发环境和工具集成起来" aria-pressed="false"><span>开发工具集成</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/language-service" title="使用 Angular 语言服务加速开发。" target="_self"><span>语言服务</span></a></div></aio-nav-item></div></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="工作空间与项目的结构，及其配置文件。" aria-pressed="false"><span>配置</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/file-structure" title="Angular 工作区在文件系统中是怎样的。" target="_self"><span>项目文件结构</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/workspace-config" title="&quot;angular.json&quot; 包含供 CLI 命令使用的工作区和项目默认配置。" target="_self"><span>工作区配置</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/npm-packages" title="开发期间和运行期间所需的 npm 包的说明。" target="_self"><span>npm 包</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/typescript-configuration" title="给 Angular 开发者的 TypeScript 配置。" target="_self"><span>TypeScript 配置</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/browser-support" title="浏览器支持与腻子脚本指南。" target="_self"><span>浏览器支持</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular 的版本发布实践、更新与升级。" aria-pressed="false"><span>发布信息</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/updating" title="如何把 Angular 应用和库升级到最新版本。" target="_self"><span>保持最新</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/releases" title="Angular 的版本、发布、支持、弃用策略及实践。" target="_self"><span>发布实践</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/updating-to-version-9" title="支持把你的应用从 8 升级到 9。" target="_self"><span>升级到第 9 版</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/deprecations" title="弃用的 Angular API 和特性汇总。" target="_self"><span>弃用清单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/ivy" title="关于 Angular Ivy 的编译与渲染管道。" target="_self"><span>Angular Ivy</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular 语法、编码、术语汇总。" aria-pressed="false"><span>快捷手册</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/cheatsheet" title="关于 Angular 常用编码技术的快速指南。" target="_self"><span>速查表</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/styleguide" title="写出 Angular 风格的程序" target="_self"><span>风格指南</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/glossary" title="Angular 中最重要的词汇的简要定义。" target="_self"><span>词汇表</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular CLI 命令参考手册。" aria-pressed="false"><span>CLI 命令</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli" title="CLI 工具介绍、命令、语法" target="_self"><span>概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/usage-analytics-gathering" title="管理员如何从用户那里收集使用情况分析。" target="_self"><span>使用情况分析</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/add" title="ng add." target="_self"><span>ng add</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/analytics" title="ng analytics." target="_self"><span>ng analytics</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/build" title="ng build." target="_self"><span>ng build</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/config" title="ng config." target="_self"><span>ng config</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/deploy" title="ng deploy." target="_self"><span>ng deploy</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/doc" title="ng doc." target="_self"><span>ng doc</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/e2e" title="ng e2e." target="_self"><span>ng e2e</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/generate" title="ng generate." target="_self"><span>ng generate</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/help" title="ng help." target="_self"><span>ng help</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/lint" title="ng lint." target="_self"><span>ng lint</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/new" title="ng new." target="_self"><span>ng new</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/run" title="ng run." target="_self"><span>ng run</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/serve" title="ng serve." target="_self"><span>ng serve</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/test" title="ng test." target="_self"><span>ng test</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div 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id="tutorial-toh-pt4"><aio-mode-banner></aio-mode-banner><aio-doc-viewer class=""><div style="opacity:1"><div class="github-links"><a href="https://github.com/angular/angular-cn/edit/aio/aio/content/tutorial/toh-pt4.md?message=docs%3A%20请简述你的修改..." aria-label="提供编辑建议" title="提供编辑建议"><i class="material-icons" aria-hidden="true" role="img">mode_edit</i></a></div><div class="content"><h1 id="create-services" translation-result="on">服务<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-services"><i class="material-icons">link</i></a></h1><aio-toc class="embedded" ng-version="9.0.0-rc.11"><div class="toc-inner no-print collapsed ng-star-inserted"><button type="button" title="Expand/collapse contents" aria-label="Expand/collapse contents" class="toc-heading embedded secondary ng-star-inserted" aria-pressed="false">目录<mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon collapsed mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><ul class="toc-list embedded"><li class="h2 ng-star-inserted" title="为什么需要服务"><a href="tutorial/toh-pt4#why-services">为什么需要服务</a></li><li class="h2 ng-star-inserted" title="创建 HeroService"><a href="tutorial/toh-pt4#create-the-heroservice">创建 <code>HeroService</code></a></li><li class="h3 ng-star-inserted" title="@Injectable() 服务"><a href="tutorial/toh-pt4#injectable-services"><code>@Injectable()</code> 服务</a></li><li class="h3 secondary ng-star-inserted" title="获取英雄数据"><a href="tutorial/toh-pt4#get-hero-data">获取英雄数据</a></li><li class="h2 secondary ng-star-inserted" title="提供（provide） HeroService"><a href="tutorial/toh-pt4#provide-the-heroservice">提供（provide） <code>HeroService</code></a></li><li class="h2 secondary ng-star-inserted" title="修改 HeroesComponent"><a href="tutorial/toh-pt4#update-heroescomponent">修改 <code>HeroesComponent</code></a></li><li class="h3 secondary ng-star-inserted" title="注入 HeroService"><a href="tutorial/toh-pt4#inject-the-heroservice">注入 <code>HeroService</code></a></li><li class="h3 secondary ng-star-inserted" title="添加 getHeroes()"><a href="tutorial/toh-pt4#add-getheroes">添加 <em>getHeroes()</em></a></li><li class="h3 secondary ng-star-inserted" title="在 ngOnInit() 中调用它"><a href="tutorial/toh-pt4#call-it-in-ngoninit">在 <code>ngOnInit()</code> 中调用它</a></li><li class="h3 secondary ng-star-inserted" title="查看运行效果"><a href="tutorial/toh-pt4#see-it-run">查看运行效果</a></li><li class="h2 secondary ng-star-inserted" title="可观察（Observable）的数据"><a href="tutorial/toh-pt4#observable-data">可观察（Observable）的数据</a></li><li class="h3 secondary ng-star-inserted" title="可观察对象版本的 HeroService"><a href="tutorial/toh-pt4#observable-heroservice">可观察对象版本的 <code>HeroService</code></a></li><li class="h3 secondary ng-star-inserted" title="在 HeroesComponent 中订阅"><a href="tutorial/toh-pt4#subscribe-in-heroescomponent">在 <code>HeroesComponent</code> 中订阅</a></li><li class="h2 secondary ng-star-inserted" title="显示消息"><a href="tutorial/toh-pt4#show-messages">显示消息</a></li><li class="h3 secondary ng-star-inserted" title="创建 MessagesComponent"><a href="tutorial/toh-pt4#create-messagescomponent">创建 <code>MessagesComponent</code></a></li><li class="h3 secondary ng-star-inserted" title="创建 MessageService"><a href="tutorial/toh-pt4#create-the-messageservice">创建 <code>MessageService</code></a></li><li class="h3 secondary ng-star-inserted" title="把它注入到 HeroService 中"><a href="tutorial/toh-pt4#inject-it-into-the-heroservice">把它注入到 <code>HeroService</code> 中</a></li><li class="h3 secondary ng-star-inserted" title="从 HeroService 中发送一条消息"><a href="tutorial/toh-pt4#send-a-message-from-heroservice">从 <code>HeroService</code> 中发送一条消息</a></li><li class="h3 secondary ng-star-inserted" title="从 HeroService 中显示消息"><a href="tutorial/toh-pt4#display-the-message-from-heroservice">从 <code>HeroService</code> 中显示消息</a></li><li class="h3 secondary ng-star-inserted" title="绑定到 MessageService"><a href="tutorial/toh-pt4#bind-to-the-messageservice">绑定到 <code>MessageService</code></a></li><li class="h2 secondary ng-star-inserted" title="为 hero 服务添加额外的消息"><a href="tutorial/toh-pt4#add-additional-messages-to-hero-service">为 hero 服务添加额外的消息</a></li><li class="h2 secondary ng-star-inserted" title="查看最终代码"><a href="tutorial/toh-pt4#final-code-review">查看最终代码</a></li><li class="h2 secondary ng-star-inserted" title="小结"><a href="tutorial/toh-pt4#summary">小结</a></li></ul><button type="button" title="Expand/collapse contents" aria-label="Expand/collapse contents" class="toc-more-items embedded material-icons collapsed ng-star-inserted" aria-pressed="false"></button></div></aio-toc><h1 translation-origin="off" id="create-services">Create services<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-services"><i class="material-icons">link</i></a></h1><p translation-result="on">英雄指南的 <code>HeroesComponent</code> 目前获取和显示的都是模拟数据。</p><p translation-origin="off">The Tour of Heroes <code>HeroesComponent</code> is currently getting and displaying fake data.</p><p translation-result="on">本节课的重构完成之后，<code>HeroesComponent</code> 变得更精简，并且聚焦于为它的视图提供支持。这也让它更容易使用模拟服务进行单元测试。</p><p translation-origin="off">After the refactoring in this tutorial, <code>HeroesComponent</code> will be lean and focused on supporting the view. It will also be easier to unit-test with a mock service.</p><h2 id="why-services" translation-result="on">为什么需要服务<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#why-services"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="why-services">Why services<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#why-services"><i class="material-icons">link</i></a></h2><p translation-result="on">组件不应该直接获取或保存数据，它们不应该了解是否在展示假数据。 它们应该聚焦于展示数据，而把数据访问的职责委托给某个服务。</p><p translation-origin="off">Components shouldn't fetch or save data directly and they certainly shouldn't knowingly present fake data. They should focus on presenting data and delegate data access to a service.</p><p translation-result="on">本节课，你将创建一个 <code>HeroService</code>，应用中的所有类都可以使用它来获取英雄列表。 不要使用 <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new"><code>new</code> 关键字</a>来创建此服务，而要依靠 Angular 的<a href="guide/dependency-injection"><em>依赖注入</em></a>机制把它注入到 <code>HeroesComponent</code> 的构造函数中。</p><p translation-origin="off">In this tutorial, you'll create a <code>HeroService</code> that all application classes can use to get heroes. Instead of creating that service with the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new"><code>new</code> keyword</a>, you'll rely on Angular <a href="guide/dependency-injection"><em>dependency injection</em></a> to inject it into the <code>HeroesComponent</code> constructor.</p><p translation-result="on">服务是在多个“互相不知道”的类之间共享信息的好办法。 你将创建一个 <code>MessageService</code>，并且把它注入到两个地方：</p><p translation-origin="off">Services are a great way to share information among classes that <em>don't know each other</em>. You'll create a <code>MessageService</code> and inject it in two places.</p><ol><li><p translation-result="on">注入到 <code>HeroService</code> 中，它会使用该服务发送消息</p><p translation-origin="off">Inject in HeroService, which uses the service to send a message.</p></li><li><p translation-result="on">注入到 <code>MessagesComponent</code> 中，它会显示其中的消息。当用户点击某个英雄时，它还会显示该英雄的 ID。</p><p translation-origin="off">Inject in MessagesComponent, which displays that message, and also displays the ID when the user clicks a hero.</p></li></ol><h2 id="create-the-heroservice" translation-result="on">创建 <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-the-heroservice"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="create-the-heroservice">Create the <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-the-heroservice"><i class="material-icons">link</i></a></h2><p translation-result="on">使用 Angular CLI 创建一个名叫 <code>hero</code> 的服务。</p><p translation-origin="off">Using the Angular CLI, create a service called <code>hero</code>.</p><code-example language="sh" class="code-shell" ng-version="9.0.0-rc.11"><div style="display:none">ng generate service hero</div><aio-code><pre class="lang-sh prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">ng generate service hero</span></code>
    </pre></aio-code></code-example><p translation-result="on">该命令会在 <code>src/app/hero.service.ts</code> 中生成 <code>HeroService</code> 类的骨架，代码如下：</p><p translation-origin="off">The command generates a skeleton <code>HeroService</code> class in <code>src/app/hero.service.ts</code> as follows:</p><code-example path="toh-pt4/src/app/hero.service.1.ts" region="new" header="src/app/hero.service.ts (new service)" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Injectable" class="code-anchor">Injectable</a> } from '@angular/core'; @<a href="api/core/Injectable" class="code-anchor">Injectable</a>({ <a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root', }) export class HeroService { constructor() { } }</div><header class="ng-star-inserted">src/app/hero.service.ts (new service)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts (new service)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Injectable" class="code-anchor"><span class="typ">Injectable</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Injectable" class="code-anchor"><span class="lit">Injectable</span></a><span class="pun">({</span><span class="pln">
  </span><a href="api/core/Injectable#providedIn" class="code-anchor"><span class="pln">providedIn</span></a><span class="pun">:</span><span class="pln"> </span><span class="str">'root'</span><span class="pun">,</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroService</span><span class="pln"> </span><span class="pun">{</span><span class="pln">

  </span><span class="kwd">constructor</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span><span class="pln">

</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><h3 id="injectable-services" translation-result="on"><code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> 服务<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#injectable-services"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="injectable-services"><code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> services<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#injectable-services"><i class="material-icons">link</i></a></h3><p translation-result="on">注意，这个新的服务导入了 Angular 的 <code><a href="api/core/Injectable" class="code-anchor">Injectable</a></code> 符号，并且给这个服务类添加了 <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> 装饰器。 它把这个类标记为<em>依赖注入系统</em>的参与者之一。<code>HeroService</code> 类将会提供一个可注入的服务，并且它还可以拥有自己的待注入的依赖。 目前它还没有依赖，但是<a href="tutorial/toh-pt4#inject-message-service">很快就会有了</a>。</p><p translation-origin="off">Notice that the new service imports the Angular <code><a href="api/core/Injectable" class="code-anchor">Injectable</a></code> symbol and annotates the class with the <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> decorator. This marks the class as one that participates in the <em>dependency injection system</em>. The <code>HeroService</code> class is going to provide an injectable service, and it can also have its own injected dependencies. It doesn't have any dependencies yet, but <a href="tutorial/toh-pt4#inject-message-service">it will soon</a>.</p><p translation-result="on"><code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> 装饰器会接受该服务的元数据对象，就像 <code>@<a href="api/core/Component" class="code-anchor">Component</a>()</code> 对组件类的作用一样。</p><p translation-origin="off">The <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> decorator accepts a metadata object for the service, the same way the <code>@<a href="api/core/Component" class="code-anchor">Component</a>()</code> decorator did for your component classes.</p><h3 id="get-hero-data" translation-result="on">获取英雄数据<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#get-hero-data"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="get-hero-data">Get hero data<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#get-hero-data"><i class="material-icons">link</i></a></h3><p translation-result="on"><code>HeroService</code> 可以从任何地方获取数据：Web 服务、本地存储（LocalStorage）或一个模拟的数据源。</p><p translation-origin="off">The <code>HeroService</code> could get hero data from anywhere—a web service, local storage, or a mock data source.</p><p translation-result="on">从组件中移除数据访问逻辑，意味着将来任何时候你都可以改变目前的实现方式，而不用改动任何组件。 这些组件不需要了解该服务的内部实现。</p><p translation-origin="off">Removing data access from components means you can change your mind about the implementation anytime, without touching any components. They don't know how the service works.</p><p translation-result="on">这节课中的实现仍然会提供<em>模拟的英雄列表</em>。</p><p translation-origin="off">The implementation in <em>this</em> tutorial will continue to deliver <em>mock heroes</em>.</p><p translation-result="on">导入 <code>Hero</code> 和 <code>HEROES</code>。</p><p translation-origin="off">Import the <code>Hero</code> and <code>HEROES</code>.</p><code-example path="toh-pt4/src/app/hero.service.ts" header="src/app/hero.service.ts" region="import-heroes" ng-version="9.0.0-rc.11"><div style="display:none">import { Hero } from './hero'; import { HEROES } from './mock-heroes';</div><header class="ng-star-inserted">src/app/hero.service.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Hero</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./hero'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> HEROES </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./mock-heroes'</span><span class="pun">;</span></code>
    </pre></aio-code></code-example><p translation-result="on">添加一个 <code>getHeroes</code> 方法，让它返回<em>模拟的英雄列表</em>。</p><p translation-origin="off">Add a <code>getHeroes</code> method to return the <em>mock heroes</em>.</p><code-example path="toh-pt4/src/app/hero.service.1.ts" header="src/app/hero.service.ts" region="getHeroes" ng-version="9.0.0-rc.11"><div style="display:none">getHeroes(): Hero[] { return HEROES; }</div><header class="ng-star-inserted">src/app/hero.service.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">[]</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">return</span><span class="pln"> HEROES</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><a id="provide"></a><h2 id="provide-the-heroservice" translation-result="on">提供（provide） <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#provide-the-heroservice"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="provide-the-heroservice">Provide the <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#provide-the-heroservice"><i class="material-icons">link</i></a></h2><p translation-result="on">你必须先注册一个<em>服务提供商</em>，来让 <code>HeroService</code> 在依赖注入系统中可用，Angular 才能把它注入到 <code>HeroesComponent</code> 中。所谓服务提供商就是某种可用来创建或交付一个服务的东西；在这里，它通过实例化 <code>HeroService</code> 类，来提供该服务。</p><p translation-origin="off">You must make the <code>HeroService</code> available to the dependency injection system before Angular can <em>inject</em> it into the <code>HeroesComponent</code> by registering a <em>provider</em>. A provider is something that can create or deliver a service; in this case, it instantiates the <code>HeroService</code> class to provide the service.</p><p translation-result="on">为了确保 <code>HeroService</code> 可以提供该服务，就要使用<em>注入器</em>来注册它。注入器是一个对象，负责当应用要求获取它的实例时选择和注入该提供商。</p><p translation-origin="off">To make sure that the <code>HeroService</code> can provide this service, register it with the <em>injector</em>, which is the object that is responsible for choosing and injecting the provider where the app requires it.</p><p translation-result="on">默认情况下，Angular CLI 命令 <code>ng generate service</code> 会通过给 <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> 装饰器添加 <code><a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root'</code> 元数据的形式，用<em>根注入器</em>将你的服务注册成为提供商。</p><p translation-origin="off">By default, the Angular CLI command <code>ng generate service</code> registers a provider with the <em>root injector</em> for your service by including provider metadata, that is <code><a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root'</code> in the <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a>()</code> decorator.</p><code-example ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Injectable" class="code-anchor">Injectable</a>({ <a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root', })</div><aio-code><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Injectable" class="code-anchor"><span class="lit">Injectable</span></a><span class="pun">({</span><span class="pln">
  </span><a href="api/core/Injectable#providedIn" class="code-anchor"><span class="pln">providedIn</span></a><span class="pun">:</span><span class="pln"> </span><span class="str">'root'</span><span class="pun">,</span><span class="pln">
</span><span class="pun">})</span></code>
    </pre></aio-code></code-example><p translation-result="on">当你在顶层提供该服务时，Angular 就会为 <code>HeroService</code> 创建一个单一的、共享的实例，并把它注入到任何想要它的类上。 在 <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a></code> 元数据中注册该提供商，还能允许 Angular 通过移除那些完全没有用过的服务来进行优化。</p><p translation-origin="off">When you provide the service at the root level, Angular creates a single, shared instance of <code>HeroService</code> and injects into any class that asks for it. Registering the provider in the <code>@<a href="api/core/Injectable" class="code-anchor">Injectable</a></code> metadata also allows Angular to optimize an app by removing the service if it turns out not to be used after all.</p><div class="alert is-helpful"><p translation-result="on">要了解关于提供商的更多知识，参见<a href="guide/providers">提供商部分</a>。 要了解关于注入器的更多知识，参见<a href="guide/dependency-injection">依赖注入指南</a>。</p><p translation-origin="off">To learn more about providers, see the <a href="guide/providers">Providers section</a>. To learn more about injectors, see the <a href="guide/dependency-injection">Dependency Injection guide</a>.</p></div><p translation-result="on">现在 <code>HeroService</code> 已经准备好插入到 <code>HeroesComponent</code> 中了。</p><p translation-origin="off">The <code>HeroService</code> is now ready to plug into the <code>HeroesComponent</code>.</p><div class="alert is-important"><p translation-result="on">这是一个过渡性的代码范例，它将会允许你提供并使用 <code>HeroService</code>。此刻的代码和<a href="tutorial/toh-pt4#final-code-review">最终代码</a>相差很大。</p><p translation-origin="off">This is an interim code sample that will allow you to provide and use the <code>HeroService</code>. At this point, the code will differ from the <code>HeroService</code> in the <a href="tutorial/toh-pt4#final-code-review">"final code review"</a>.</p></div><h2 id="update-heroescomponent" translation-result="on">修改 <code>HeroesComponent</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#update-heroescomponent"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="update-heroescomponent">Update <code>HeroesComponent</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#update-heroescomponent"><i class="material-icons">link</i></a></h2><p translation-result="on">打开 <code>HeroesComponent</code> 类文件。</p><p translation-origin="off">Open the <code>HeroesComponent</code> class file.</p><p translation-result="on">删除 <code>HEROES</code> 的导入语句，因为你以后不会再用它了。 转而导入 <code>HeroService</code>。</p><p translation-origin="off">Delete the <code>HEROES</code> import, because you won't need that anymore. Import the <code>HeroService</code> instead.</p><code-example path="toh-pt4/src/app/heroes/heroes.component.ts" header="src/app/heroes/heroes.component.ts (import HeroService)" region="hero-service-import" ng-version="9.0.0-rc.11"><div style="display:none">import { HeroService } from '../hero.service'; import { MessageService } from '../message.service';</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts (import HeroService)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts (import HeroService)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">HeroService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'../hero.service'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'../message.service'</span><span class="pun">;</span></code>
    </pre></aio-code></code-example><p translation-result="on">把 <code>heroes</code> 属性的定义改为一句简单的声明。</p><p translation-origin="off">Replace the definition of the <code>heroes</code> property with a simple declaration.</p><code-example path="toh-pt4/src/app/heroes/heroes.component.ts" header="src/app/heroes/heroes.component.ts" region="heroes" ng-version="9.0.0-rc.11"><div style="display:none">heroes: Hero[];</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">heroes</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">[];</span></code>
    </pre></aio-code></code-example><a id="inject"></a><h3 id="inject-the-heroservice" translation-result="on">注入 <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#inject-the-heroservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="inject-the-heroservice">Inject the <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#inject-the-heroservice"><i class="material-icons">link</i></a></h3><p translation-result="on">往构造函数中添加一个私有的 <code>heroService</code>，其类型为 <code>HeroService</code>。</p><p translation-origin="off">Add a private <code>heroService</code> parameter of type <code>HeroService</code> to the constructor.</p><code-example path="toh-pt4/src/app/heroes/heroes.component.ts" header="src/app/heroes/heroes.component.ts" region="ctor" ng-version="9.0.0-rc.11"><div style="display:none">constructor(private heroService: HeroService, private messageService: MessageService) { }</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">private</span><span class="pln"> heroService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">HeroService</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">private</span><span class="pln"> messageService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">这个参数同时做了两件事：1. 声明了一个私有 <code>heroService</code> 属性，2. 把它标记为一个 <code>HeroService</code> 的注入点。</p><p translation-origin="off">The parameter simultaneously defines a private <code>heroService</code> property and identifies it as a <code>HeroService</code> injection site.</p><p translation-result="on">当 Angular 创建 <code>HeroesComponent</code> 时，<a href="guide/dependency-injection">依赖注入</a>系统就会把这个 <code>heroService</code> 参数设置为 <code>HeroService</code> 的单例对象。</p><p translation-origin="off">When Angular creates a <code>HeroesComponent</code>, the <a href="guide/dependency-injection">Dependency Injection</a> system sets the <code>heroService</code> parameter to the singleton instance of <code>HeroService</code>.</p><h3 id="add-getheroes" translation-result="on">添加 <em>getHeroes()</em><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#add-getheroes"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="add-getheroes">Add <code>getHeroes()</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#add-getheroes"><i class="material-icons">link</i></a></h3><p translation-result="on">创建一个函数，以从服务中获取这些英雄数据。</p><p translation-origin="off">Create a function to retrieve the heroes from the service.</p><code-example path="toh-pt4/src/app/heroes/heroes.component.1.ts" header="src/app/heroes/heroes.component.ts" region="getHeroes" ng-version="9.0.0-rc.11"><div style="display:none">getHeroes(): void { this.heroes = this.heroService.getHeroes(); }</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroService</span><span class="pun">.</span><span class="pln">getHeroes</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><a id="oninit"></a><h3 id="call-it-in-ngoninit" translation-result="on">在 <code>ngOnInit()</code> 中调用它<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#call-it-in-ngoninit"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="call-it-in-ngoninit">Call it in <code>ngOnInit()</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#call-it-in-ngoninit"><i class="material-icons">link</i></a></h3><p translation-result="on">你固然可以在构造函数中调用 <code>getHeroes()</code>，但那不是最佳实践。</p><p translation-origin="off">While you could call <code>getHeroes()</code> in the constructor, that's not the best practice.</p><p translation-result="on">让构造函数保持简单，只做初始化操作，比如把构造函数的参数赋值给属性。 构造函数不应该<em>做任何事</em>。 它当然不应该调用某个函数来向远端服务（比如真实的数据服务）发起 HTTP 请求。</p><p translation-origin="off">Reserve the constructor for simple initialization such as wiring constructor parameters to properties. The constructor shouldn't <em>do anything</em>. It certainly shouldn't call a function that makes HTTP requests to a remote server as a <em>real</em> data service would.</p><p translation-result="on">而是选择在 <a href="guide/lifecycle-hooks"><em>ngOnInit 生命周期钩子</em></a>中调用 <code>getHeroes()</code>，之后 Angular 会在构造出 <code>HeroesComponent</code> 的实例之后的某个合适的时机调用 <code>ngOnInit()</code>。</p><p translation-origin="off">Instead, call <code>getHeroes()</code> inside the <a href="guide/lifecycle-hooks"><em>ngOnInit lifecycle hook</em></a> and let Angular call <code>ngOnInit()</code> at an appropriate time <em>after</em> constructing a <code>HeroesComponent</code> instance.</p><code-example path="toh-pt4/src/app/heroes/heroes.component.ts" header="src/app/heroes/heroes.component.ts" region="ng-on-init" ng-version="9.0.0-rc.11"><div style="display:none">ngOnInit() { this.getHeroes(); }</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">ngOnInit</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">getHeroes</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><h3 id="see-it-run" translation-result="on">查看运行效果<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#see-it-run"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="see-it-run">See it run<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#see-it-run"><i class="material-icons">link</i></a></h3><p translation-result="on">刷新浏览器，该应用仍运行的一如既往。 显示英雄列表，并且当你点击某个英雄的名字时显示出英雄详情视图。</p><p translation-origin="off">After the browser refreshes, the app should run as before, showing a list of heroes and a hero detail view when you click on a hero name.</p><h2 id="observable-data" translation-result="on">可观察（Observable）的数据<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#observable-data"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="observable-data">Observable data<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#observable-data"><i class="material-icons">link</i></a></h2><p translation-result="on"><code>HeroService.getHeroes()</code> 的函数签名是<em>同步的</em>，它所隐含的假设是 <code>HeroService</code> 总是能同步获取英雄列表数据。 而 <code>HeroesComponent</code> 也同样假设能同步取到 <code>getHeroes()</code> 的结果。</p><p translation-origin="off">The <code>HeroService.getHeroes()</code> method has a <em>synchronous signature</em>, which implies that the <code>HeroService</code> can fetch heroes synchronously. The <code>HeroesComponent</code> consumes the <code>getHeroes()</code> result as if heroes could be fetched synchronously.</p><code-example path="toh-pt4/src/app/heroes/heroes.component.1.ts" header="src/app/heroes/heroes.component.ts" region="get-heroes" ng-version="9.0.0-rc.11"><div style="display:none">this.heroes = this.heroService.getHeroes();</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroService</span><span class="pun">.</span><span class="pln">getHeroes</span><span class="pun">();</span></code>
    </pre></aio-code></code-example><p translation-result="on">这在真实的应用中几乎是不可能的。 现在能这么做，只是因为目前该服务返回的是<em>模拟数据</em>。 不过很快，该应用就要从远端服务器获取英雄数据了，而那天生就是<em>异步</em>操作。</p><p translation-origin="off">This will not work in a real app. You're getting away with it now because the service currently returns <em>mock heroes</em>. But soon the app will fetch heroes from a remote server, which is an inherently <em>asynchronous</em> operation.</p><p translation-result="on"><code>HeroService</code> 必须等服务器给出响应， 而 <code>getHeroes()</code> 不能立即返回英雄数据， 浏览器也不会在该服务等待期间停止响应。</p><p translation-origin="off">The <code>HeroService</code> must wait for the server to respond, <code>getHeroes()</code> cannot return immediately with hero data, and the browser will not block while the service waits.</p><p translation-result="on"><code>HeroService.getHeroes()</code> 必须具有某种形式的<em>异步函数签名</em>。</p><p translation-origin="off"><code>HeroService.getHeroes()</code> must have an <em>asynchronous signature</em> of some kind.</p><p translation-result="on">这节课，<code>HeroService.getHeroes()</code> 将会返回 <code>Observable</code>，部分原因在于它最终会使用 Angular 的 <code>HttpClient.get</code> 方法来获取英雄数据，而 <a href="guide/http"><code>HttpClient.get()</code> 会返回 <code>Observable</code></a>。</p><p translation-origin="off">In this tutorial, <code>HeroService.getHeroes()</code> will return an <code>Observable</code> because it will eventually use the Angular <code>HttpClient.get</code> method to fetch the heroes and <a href="guide/http"><code>HttpClient.get()</code> returns an <code>Observable</code></a>.</p><h3 id="observable-heroservice" translation-result="on">可观察对象版本的 <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#observable-heroservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="observable-heroservice">Observable <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#observable-heroservice"><i class="material-icons">link</i></a></h3><p translation-result="on"><code>Observable</code> 是 <a href="http://reactivex.io/rxjs/">RxJS 库</a>中的一个关键类。</p><p translation-origin="off"><code>Observable</code> is one of the key classes in the <a href="http://reactivex.io/rxjs/">RxJS library</a>.</p><p translation-result="on">在<a href="tutorial/toh-pt6">稍后的 HTTP 教程</a>中，你就会知道 Angular <code><a href="api/common/http/HttpClient" class="code-anchor">HttpClient</a></code> 的方法会返回 RxJS 的 <code>Observable</code>。 这节课，你将使用 RxJS 的 <code>of()</code> 函数来模拟从服务器返回数据。</p><p translation-origin="off">In a <a href="tutorial/toh-pt6">later tutorial on HTTP</a>, you'll learn that Angular's <code><a href="api/common/http/HttpClient" class="code-anchor">HttpClient</a></code> methods return RxJS <code>Observable</code>s. In this tutorial, you'll simulate getting data from the server with the RxJS <code>of()</code> function.</p><p translation-result="on">打开 <code>HeroService</code> 文件，并从 RxJS 中导入 <code>Observable</code> 和 <code>of</code> 符号。</p><p translation-origin="off">Open the <code>HeroService</code> file and import the <code>Observable</code> and <code>of</code> symbols from RxJS.</p><code-example path="toh-pt4/src/app/hero.service.ts" header="src/app/hero.service.ts (Observable imports)" region="import-observable" ng-version="9.0.0-rc.11"><div style="display:none">import { Observable, of } from 'rxjs';</div><header class="ng-star-inserted">src/app/hero.service.ts (Observable imports)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts (Observable imports)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Observable</span><span class="pun">,</span><span class="pln"> of </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'rxjs'</span><span class="pun">;</span></code>
    </pre></aio-code></code-example><p translation-result="on">把 <code>getHeroes()</code> 方法改成这样：</p><p translation-origin="off">Replace the <code>getHeroes()</code> method with the following:</p><code-example path="toh-pt4/src/app/hero.service.ts" header="src/app/hero.service.ts" region="getHeroes-1" ng-version="9.0.0-rc.11"><div style="display:none">getHeroes(): Observable&lt;Hero[]&gt; { return of(HEROES); }</div><header class="ng-star-inserted">src/app/hero.service.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="typ">Observable</span><span class="pun">&lt;</span><span class="typ">Hero</span><span class="pun">[]&gt;</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">return</span><span class="pln"> of</span><span class="pun">(</span><span class="pln">HEROES</span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on"><code>of(HEROES)</code> 会返回一个 <code>Observable&lt;Hero[]&gt;</code>，它会发出单个值，这个值就是这些模拟英雄的数组。</p><p translation-origin="off"><code>of(HEROES)</code> returns an <code>Observable&lt;Hero[]&gt;</code> that emits <em>a single value</em>, the array of mock heroes.</p><div class="alert is-helpful"><p translation-result="on">在 <a href="tutorial/toh-pt6">HTTP 教程</a>中，你将会调用 <code>HttpClient.get&lt;Hero[]&gt;()</code> 它也同样返回一个 <code>Observable&lt;Hero[]&gt;</code>，它也会发出单个值，这个值就是来自 HTTP 响应体中的英雄数组。</p><p translation-origin="off">In the <a href="tutorial/toh-pt6">HTTP tutorial</a>, you'll call <code>HttpClient.get&lt;Hero[]&gt;()</code> which also returns an <code>Observable&lt;Hero[]&gt;</code> that emits <em>a single value</em>, an array of heroes from the body of the HTTP response.</p></div><h3 id="subscribe-in-heroescomponent" translation-result="on">在 <code>HeroesComponent</code> 中订阅<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#subscribe-in-heroescomponent"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="subscribe-in-heroescomponent">Subscribe in <code>HeroesComponent</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#subscribe-in-heroescomponent"><i class="material-icons">link</i></a></h3><p translation-result="on"><code>HeroService.getHeroes</code> 方法之前返回一个 <code>Hero[]</code>， 现在它返回的是 <code>Observable&lt;Hero[]&gt;</code>。</p><p translation-origin="off">The <code>HeroService.getHeroes</code> method used to return a <code>Hero[]</code>. Now it returns an <code>Observable&lt;Hero[]&gt;</code>.</p><p translation-result="on">你必须在 <code>HeroesComponent</code> 中也向本服务中的这种形式看齐。</p><p translation-origin="off">You'll have to adjust to that difference in <code>HeroesComponent</code>.</p><p translation-result="on">找到 <code>getHeroes</code> 方法，并且把它替换为如下代码（和前一个版本对比显示）：</p><p translation-origin="off">Find the <code>getHeroes</code> method and replace it with the following code (shown side-by-side with the previous version for comparison)</p><code-tabs ng-version="9.0.0-rc.11"><div style="display:none"><code-pane header="heroes.component.ts (Observable)" path="toh-pt4/src/app/heroes/heroes.component.ts" region="getHeroes">getHeroes(): void { this.heroService.getHeroes() .subscribe(heroes =&gt; this.heroes = heroes); }</code-pane><code-pane header="heroes.component.ts (Original)" path="toh-pt4/src/app/heroes/heroes.component.1.ts" region="getHeroes">getHeroes(): void { this.heroes = this.heroService.getHeroes(); }</code-pane></div><mat-card class="mat-card"><mat-tab-group class="mat-tab-group code-tab-group mat-primary"><mat-tab-header class="mat-tab-header"><div aria-hidden="true" mat-ripple="" class="mat-ripple mat-tab-header-pagination mat-tab-header-pagination-before mat-elevation-z4 mat-tab-header-pagination-disabled"><div class="mat-tab-header-pagination-chevron"></div></div><div class="mat-tab-label-container"><div role="tablist" class="mat-tab-list" style="transform:translateX(0)"><div class="mat-tab-labels"><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label mat-tab-label-active ng-star-inserted" id="mat-tab-label-0-0" tabindex="0" aria-posinset="1" aria-setsize="2" aria-controls="mat-tab-content-0-0" aria-selected="true" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">heroes.component.ts (Observable)</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-0-1" tabindex="-1" aria-posinset="2" aria-setsize="2" aria-controls="mat-tab-content-0-1" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">heroes.component.ts (Original)</span></div></div></div><mat-ink-bar class="mat-ink-bar" style="visibility:visible;left:0;width:264px"></mat-ink-bar></div></div><div aria-hidden="true" mat-ripple="" class="mat-ripple mat-tab-header-pagination mat-tab-header-pagination-after mat-elevation-z4 mat-tab-header-pagination-disabled"><div class="mat-tab-header-pagination-chevron"></div></div></mat-tab-header><div class="mat-tab-body-wrapper"><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-2 mat-tab-body-active ng-star-inserted" id="mat-tab-content-0-0" aria-labelledby="mat-tab-label-0-0"><div class="mat-tab-body-content ng-tns-c50-2 ng-trigger ng-trigger-translateTab" style="transform:none"><aio-code class="ng-star-inserted" style=""><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from heroes.component.ts (Observable)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroService</span><span class="pun">.</span><span class="pln">getHeroes</span><span class="pun">()</span><span class="pln">
      </span><span class="pun">.</span><span class="pln">subscribe</span><span class="pun">(</span><span class="pln">heroes </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes </span><span class="pun">=</span><span class="pln"> heroes</span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-3 ng-star-inserted" id="mat-tab-content-0-1" aria-labelledby="mat-tab-label-0-1"><div class="mat-tab-body-content ng-tns-c50-3 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body></div></mat-tab-group></mat-card></code-tabs><p translation-result="on"><code>Observable.subscribe()</code> 是关键的差异点。</p><p translation-origin="off"><code>Observable.subscribe()</code> is the critical difference.</p><p translation-result="on">上一个版本把英雄的数组赋值给了该组件的 <code>heroes</code> 属性。 这种赋值是<em>同步</em>的，这里包含的假设是服务器能立即返回英雄数组或者浏览器能在等待服务器响应时冻结界面。</p><p translation-origin="off">The previous version assigns an array of heroes to the component's <code>heroes</code> property. The assignment occurs <em>synchronously</em>, as if the server could return heroes instantly or the browser could freeze the UI while it waited for the server's response.</p><p translation-result="on">当 <code>HeroService</code> 真的向远端服务器发起请求时，这种方式就行不通了。</p><p translation-origin="off">That <em>won't work</em> when the <code>HeroService</code> is actually making requests of a remote server.</p><p translation-result="on">新的版本等待 <code>Observable</code> 发出这个英雄数组，这可能立即发生，也可能会在几分钟之后。 然后，<code>subscribe()</code> 方法把这个英雄数组传给这个回调函数，该函数把英雄数组赋值给组件的 <code>heroes</code> 属性。</p><p translation-origin="off">The new version waits for the <code>Observable</code> to emit the array of heroes—which could happen now or several minutes from now. The <code>subscribe()</code> method passes the emitted array to the callback, which sets the component's <code>heroes</code> property.</p><p translation-result="on">使用这种异步方式，当 <code>HeroService</code> 从远端服务器获取英雄数据时，就<em>可以工作了</em>。</p><p translation-origin="off">This asynchronous approach <em>will work</em> when the <code>HeroService</code> requests heroes from the server.</p><h2 id="show-messages" translation-result="on">显示消息<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#show-messages"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="show-messages">Show messages<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#show-messages"><i class="material-icons">link</i></a></h2><p translation-result="on">这一节将指导你：</p><p translation-origin="off">This section guides you through the following:</p><ul><li><p translation-result="on">添加一个 <code>MessagesComponent</code>，它在屏幕的底部显示应用中的消息。</p><p translation-origin="off">adding a <code>MessagesComponent</code> that displays app messages at the bottom of the screen</p></li><li><p translation-result="on">创建一个可注入的、全应用级别的 <code>MessageService</code>，用于发送要显示的消息。</p><p translation-origin="off">creating an injectable, app-wide <code>MessageService</code> for sending messages to be displayed</p></li><li><p translation-result="on">把 <code>MessageService</code> 注入到 <code>HeroService</code> 中。</p><p translation-origin="off">injecting <code>MessageService</code> into the <code>HeroService</code></p></li><li><p translation-result="on">当 <code>HeroService</code> 成功获取了英雄数据时显示一条消息。</p><p translation-origin="off">displaying a message when <code>HeroService</code> fetches heroes successfully</p></li></ul><h3 id="create-messagescomponent" translation-result="on">创建 <code>MessagesComponent</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-messagescomponent"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="create-messagescomponent">Create <code>MessagesComponent</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-messagescomponent"><i class="material-icons">link</i></a></h3><p translation-result="on">使用 CLI 创建 <code>MessagesComponent</code>。</p><p translation-origin="off">Use the CLI to create the <code>MessagesComponent</code>.</p><code-example language="sh" class="code-shell" ng-version="9.0.0-rc.11"><div style="display:none">ng generate component messages</div><aio-code><pre class="lang-sh prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">ng generate component messages</span></code>
    </pre></aio-code></code-example><p translation-result="on">CLI 在 <code>src/app/<a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a></code> 中创建了组件文件，并且把 <code>MessagesComponent</code> 声明在了 <code>AppModule</code> 中。</p><p translation-origin="off">The CLI creates the component files in the <code>src/app/<a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a></code> folder and declares the <code>MessagesComponent</code> in <code>AppModule</code>.</p><p translation-result="on">修改 <code>AppComponent</code> 的模板来显示所生成的 <code>MessagesComponent</code>：</p><p translation-origin="off">Modify the <code>AppComponent</code> template to display the generated <code>MessagesComponent</code>.</p><code-example header="src/app/app.component.html" path="toh-pt4/src/app/app.component.html" ng-version="9.0.0-rc.11"><div style="display:none">&lt;h1&gt;{{title}}&lt;/h1&gt; &lt;app-heroes&gt;&lt;/app-heroes&gt; &lt;app-messages&gt;&lt;/app-messages&gt;</div><header class="ng-star-inserted">src/app/app.component.html</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/app.component.html">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="tag">&lt;h1&gt;</span><span class="pln">{{title}}</span><span class="tag">&lt;/h1&gt;</span><span class="pln">
</span><span class="tag">&lt;app-heroes&gt;&lt;/app-heroes&gt;</span><span class="pln">
</span><span class="tag">&lt;app-messages&gt;&lt;/app-messages&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">你可以在页面的底部看到来自的 <code>MessagesComponent</code> 的默认内容。</p><p translation-origin="off">You should see the default paragraph from <code>MessagesComponent</code> at the bottom of the page.</p><h3 id="create-the-messageservice" translation-result="on">创建 <code>MessageService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-the-messageservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="create-the-messageservice">Create the <code>MessageService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#create-the-messageservice"><i class="material-icons">link</i></a></h3><p translation-result="on">使用 CLI 在 <code>src/app</code> 中创建 <code>MessageService</code>。</p><p translation-origin="off">Use the CLI to create the <code>MessageService</code> in <code>src/app</code>.</p><code-example language="sh" class="code-shell" ng-version="9.0.0-rc.11"><div style="display:none">ng generate service message</div><aio-code><pre class="lang-sh prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">ng generate service message</span></code>
    </pre></aio-code></code-example><p translation-result="on">打开 <code>MessageService</code>，并把它的内容改成这样：</p><p translation-origin="off">Open <code>MessageService</code> and replace its contents with the following.</p><code-example header="src/app/message.service.ts" path="toh-pt4/src/app/message.service.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Injectable" class="code-anchor">Injectable</a> } from '@angular/core'; @<a href="api/core/Injectable" class="code-anchor">Injectable</a>({ <a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root', }) export class MessageService { <a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a>: string[] = []; add(<a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>: string) { this.messages.push(<a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>); } clear() { this.messages = []; } }</div><header class="ng-star-inserted">src/app/message.service.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/message.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Injectable" class="code-anchor"><span class="typ">Injectable</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Injectable" class="code-anchor"><span class="lit">Injectable</span></a><span class="pun">({</span><span class="pln">
  </span><a href="api/core/Injectable#providedIn" class="code-anchor"><span class="pln">providedIn</span></a><span class="pun">:</span><span class="pln"> </span><span class="str">'root'</span><span class="pun">,</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><a href="api/service-worker/SwPush#messages" class="code-anchor"><span class="pln">messages</span></a><span class="pun">:</span><span class="pln"> </span><span class="kwd">string</span><span class="pun">[]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[];</span><span class="pln">

  </span><span class="kwd">add</span><span class="pun">(</span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="pln">message</span></a><span class="pun">:</span><span class="pln"> </span><span class="kwd">string</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messages</span><span class="pun">.</span><span class="pln">push</span><span class="pun">(</span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="pln">message</span></a><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

  clear</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messages </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[];</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">该服务对外暴露了它的 <code><a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a></code> 缓存，以及两个方法：<code>add()</code> 方法往缓存中添加一条消息，<code><a href="api/forms/FormArray#clear" class="code-anchor">clear()</a></code> 方法用于清空缓存。</p><p translation-origin="off">The service exposes its cache of <code><a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a></code> and two methods: one to <code>add()</code> a message to the cache and another to <code><a href="api/forms/FormArray#clear" class="code-anchor">clear()</a></code> the cache.</p><a id="inject-message-service"></a><h3 id="inject-it-into-the-heroservice" translation-result="on">把它注入到 <code>HeroService</code> 中<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#inject-it-into-the-heroservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="inject-it-into-the-heroservice">Inject it into the <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#inject-it-into-the-heroservice"><i class="material-icons">link</i></a></h3><p translation-result="on">在 <code>HeroService</code> 中导入 <code>MessageService</code>。</p><p translation-origin="off">In <code>HeroService</code>, import the <code>MessageService</code>.</p><code-example header="src/app/hero.service.ts (import MessageService)" path="toh-pt4/src/app/hero.service.ts" region="import-message-service" ng-version="9.0.0-rc.11"><div style="display:none">import { MessageService } from './message.service';</div><header class="ng-star-inserted">src/app/hero.service.ts (import MessageService)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts (import MessageService)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./message.service'</span><span class="pun">;</span></code>
    </pre></aio-code></code-example><p translation-result="on">修改这个构造函数，添加一个私有的 <code>messageService</code> 属性参数。 Angular 将会在创建 <code>HeroService</code> 时把 <code>MessageService</code> 的单例注入到这个属性中。</p><p translation-origin="off">Modify the constructor with a parameter that declares a private <code>messageService</code> property. Angular will inject the singleton <code>MessageService</code> into that property when it creates the <code>HeroService</code>.</p><code-example path="toh-pt4/src/app/hero.service.ts" header="src/app/hero.service.ts" region="ctor" ng-version="9.0.0-rc.11"><div style="display:none">constructor(private messageService: MessageService) { }</div><header class="ng-star-inserted">src/app/hero.service.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">private</span><span class="pln"> messageService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span></code>
    </pre></aio-code></code-example><div class="alert is-helpful"><p translation-result="on">这是一个典型的“服务中的服务”场景： 你把 <code>MessageService</code> 注入到了 <code>HeroService</code> 中，而 <code>HeroService</code> 又被注入到了 <code>HeroesComponent</code> 中。</p><p translation-origin="off">This is a typical "<em>service-in-service</em>" scenario: you inject the <code>MessageService</code> into the <code>HeroService</code> which is injected into the <code>HeroesComponent</code>.</p></div><h3 id="send-a-message-from-heroservice" translation-result="on">从 <code>HeroService</code> 中发送一条消息<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#send-a-message-from-heroservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="send-a-message-from-heroservice">Send a message from <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#send-a-message-from-heroservice"><i class="material-icons">link</i></a></h3><p translation-result="on">修改 <code>getHeroes()</code> 方法，在获取到英雄数组时发送一条消息。</p><p translation-origin="off">Modify the <code>getHeroes()</code> method to send a message when the heroes are fetched.</p><code-example path="toh-pt4/src/app/hero.service.ts" header="src/app/hero.service.ts" region="getHeroes" ng-version="9.0.0-rc.11"><div style="display:none">getHeroes(): Observable&lt;Hero[]&gt; { // TODO: send the <a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a> _after_ fetching the heroes this.messageService.add('HeroService: fetched heroes'); return of(HEROES); }</div><header class="ng-star-inserted">src/app/hero.service.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="typ">Observable</span><span class="pun">&lt;</span><span class="typ">Hero</span><span class="pun">[]&gt;</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="com">// TODO: send the </span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="com">message</span></a><span class="com"> _after_ fetching the heroes</span><span class="pln">
  </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messageService</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">'HeroService: fetched heroes'</span><span class="pun">);</span><span class="pln">
  </span><span class="kwd">return</span><span class="pln"> of</span><span class="pun">(</span><span class="pln">HEROES</span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><h3 id="display-the-message-from-heroservice" translation-result="on">从 <code>HeroService</code> 中显示消息<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#display-the-message-from-heroservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="display-the-message-from-heroservice">Display the message from <code>HeroService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#display-the-message-from-heroservice"><i class="material-icons">link</i></a></h3><p translation-result="on"><code>MessagesComponent</code> 可以显示所有消息， 包括当 <code>HeroService</code> 获取到英雄数据时发送的那条。</p><p translation-origin="off">The <code>MessagesComponent</code> should display all messages, including the message sent by the <code>HeroService</code> when it fetches heroes.</p><p translation-result="on">打开 <code>MessagesComponent</code>，并且导入 <code>MessageService</code>。</p><p translation-origin="off">Open <code>MessagesComponent</code> and import the <code>MessageService</code>.</p><code-example header="src/app/messages/messages.component.ts (import MessageService)" path="toh-pt4/src/app/messages/messages.component.ts" region="import-message-service" ng-version="9.0.0-rc.11"><div style="display:none">import { MessageService } from '../message.service';</div><header class="ng-star-inserted">src/app/messages/messages.component.ts (import MessageService)</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/messages/messages.component.ts (import MessageService)">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'../message.service'</span><span class="pun">;</span></code>
    </pre></aio-code></code-example><p translation-result="on">修改构造函数，添加一个 <strong>public</strong> 的 <code>messageService</code> 属性。 Angular 将会在创建 <code>MessagesComponent</code> 的实例时 把 <code>MessageService</code> 的实例注入到这个属性中。</p><p translation-origin="off">Modify the constructor with a parameter that declares a <strong>public</strong> <code>messageService</code> property. Angular will inject the singleton <code>MessageService</code> into that property when it creates the <code>MessagesComponent</code>.</p><code-example path="toh-pt4/src/app/messages/messages.component.ts" header="src/app/messages/messages.component.ts" region="ctor" ng-version="9.0.0-rc.11"><div style="display:none">constructor(public messageService: MessageService) {}</div><header class="ng-star-inserted">src/app/messages/messages.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/messages/messages.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">public</span><span class="pln"> messageService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{}</span></code>
    </pre></aio-code></code-example><p translation-result="on">这个 <code>messageService</code> 属性必须是公共属性，因为你将会在模板中绑定到它。</p><p translation-origin="off">The <code>messageService</code> property <strong>must be public</strong> because you're going to bind to it in the template.</p><div class="alert is-important"><p translation-result="on">Angular 只会绑定到组件的<em>公共</em>属性。</p><p translation-origin="off">Angular only binds to <em>public</em> component properties.</p></div><h3 id="bind-to-the-messageservice" translation-result="on">绑定到 <code>MessageService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#bind-to-the-messageservice"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="bind-to-the-messageservice">Bind to the <code>MessageService</code><a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#bind-to-the-messageservice"><i class="material-icons">link</i></a></h3><p translation-result="on">把 CLI 生成的 <code>MessagesComponent</code> 的模板改成这样：</p><p translation-origin="off">Replace the CLI-generated <code>MessagesComponent</code> template with the following.</p><code-example header="src/app/messages/messages.component.html" path="toh-pt4/src/app/messages/messages.component.html" ng-version="9.0.0-rc.11"><div style="display:none">&lt;div *<a href="api/common/NgIf" class="code-anchor">ngIf</a>="messageService.messages.length"&gt; &lt;h2&gt;Messages&lt;/h2&gt; &lt;button class="clear" (click)="messageService.clear()"&gt;clear&lt;/button&gt; &lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>='let <a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a> of messageService.messages'&gt; {{<a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>}} &lt;/div&gt; &lt;/div&gt;</div><header class="ng-star-inserted">src/app/messages/messages.component.html</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/messages/messages.component.html">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="tag">&lt;div</span><span class="pln"> *</span><a href="api/common/NgIf" class="code-anchor"><span class="atn">ngIf</span></a><span class="pun">=</span><span class="atv">"messageService.messages.length"</span><span class="tag">&gt;</span><span class="pln">

  </span><span class="tag">&lt;h2&gt;</span><span class="pln">Messages</span><span class="tag">&lt;/h2&gt;</span><span class="pln">
  </span><span class="tag">&lt;button</span><span class="pln"> </span><span class="atn">class</span><span class="pun">=</span><span class="atv">"clear"</span><span class="pln">
          (</span><span class="atn">click</span><span class="pln">)</span><span class="pun">=</span><span class="atv">"messageService.clear()"</span><span class="tag">&gt;</span><span class="pln">clear</span><span class="tag">&lt;/button&gt;</span><span class="pln">
  </span><span class="tag">&lt;div</span><span class="pln"> *</span><a href="api/common/NgForOf" class="code-anchor"><span class="atn">ngFor</span></a><span class="pun">=</span><span class="atv">'let </span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="atv">message</span></a><span class="atv"> of messageService.messages'</span><span class="tag">&gt;</span><span class="pln"> {{</span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="pln">message</span></a><span class="pln">}} </span><span class="tag">&lt;/div&gt;</span><span class="pln">

</span><span class="tag">&lt;/div&gt;</span></code>
    </pre></aio-code></code-example><p translation-result="on">这个模板直接绑定到了组件的 <code>messageService</code> 属性上。</p><p translation-origin="off">This template binds directly to the component's <code>messageService</code>.</p><ul><li><p translation-result="on"> <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 只有在有消息时才会显示消息区。</p><p translation-origin="off">The <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> only displays the messages area if there are messages to show.</p></li><li><p translation-result="on"> <code>*<a href="api/common/NgForOf" class="code-anchor">ngFor</a></code> 用来在一系列 <code>&lt;div&gt;</code> 元素中展示消息列表。</p><p translation-origin="off">An <code>*<a href="api/common/NgForOf" class="code-anchor">ngFor</a></code> presents the list of messages in repeated <code>&lt;div&gt;</code> elements.</p></li><li><p translation-result="on">Angular 的<a href="guide/template-syntax#event-binding">事件绑定</a>把按钮的 <code>click</code> 事件绑定到了 <code>MessageService.clear()</code>。</p><p translation-origin="off">An Angular <a href="guide/template-syntax#event-binding">event binding</a> binds the button's click event to <code>MessageService.clear()</code>.</p></li></ul><p translation-result="on">当你把 <a href="tutorial/toh-pt4#final-code-review">最终代码</a> 某一页的内容添加到 <code>messages.component.css</code> 中时，这些消息会变得好看一些。</p><p translation-origin="off">The messages will look better when you add the private CSS styles to <code>messages.component.css</code> as listed in one of the <a href="tutorial/toh-pt4#final-code-review">"final code review"</a> tabs below.</p><h2 id="add-additional-messages-to-hero-service" translation-result="on">为 hero 服务添加额外的消息<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#add-additional-messages-to-hero-service"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="add-additional-messages-to-hero-service">Add additional messages to hero service<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#add-additional-messages-to-hero-service"><i class="material-icons">link</i></a></h2><p translation-result="on">下面的例子展示了当用户点击某个英雄时，如何发送和显示一条消息，以及如何显示该用户的选取历史。当你学到后面的<a href="tutorial/toh-pt5">路由</a>一章时，这会很有帮助。</p><p translation-origin="off">The following example shows how to send and display a message each time the user clicks on a hero, showing a history of the user's selections. This will be helpful when you get to the next section on <a href="tutorial/toh-pt5">Routing</a>.</p><code-example header="src/app/heroes/heroes.component.ts" path="toh-pt4/src/app/heroes/heroes.component.ts" ng-version="9.0.0-rc.11"><div style="display:none">import { <a href="api/core/Component" class="code-anchor">Component</a>, <a href="api/core/OnInit" class="code-anchor">OnInit</a> } from '@angular/core'; import { Hero } from '../hero'; import { HeroService } from '../hero.service'; import { MessageService } from '../message.service'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-heroes', <a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a>: './heroes.component.html', <a href="api/core/Component#styleUrls" class="code-anchor">styleUrls</a>: ['./heroes.component.css'] }) export class HeroesComponent implements <a href="api/core/OnInit" class="code-anchor">OnInit</a> { selectedHero: Hero; heroes: Hero[]; constructor(private heroService: HeroService, private messageService: MessageService) { } ngOnInit() { this.getHeroes(); } onSelect(hero: Hero): void { this.selectedHero = hero; this.messageService.add(`HeroService: Selected hero id=${hero.id}`); } getHeroes(): void { this.heroService.getHeroes() .subscribe(heroes =&gt; this.heroes = heroes); } }</div><header class="ng-star-inserted">src/app/heroes/heroes.component.ts</header><aio-code class="headed-code"><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/heroes/heroes.component.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Component" class="code-anchor"><span class="typ">Component</span></a><span class="pun">,</span><span class="pln"> </span><a href="api/core/OnInit" class="code-anchor"><span class="typ">OnInit</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Hero</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'../hero'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">HeroService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'../hero.service'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'../message.service'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-heroes'</span><span class="pun">,</span><span class="pln">
  </span><a href="api/core/Component#templateUrl" class="code-anchor"><span class="pln">templateUrl</span></a><span class="pun">:</span><span class="pln"> </span><span class="str">'./heroes.component.html'</span><span class="pun">,</span><span class="pln">
  </span><a href="api/core/Component#styleUrls" class="code-anchor"><span class="pln">styleUrls</span></a><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">'./heroes.component.css'</span><span class="pun">]</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroesComponent</span><span class="pln"> </span><span class="kwd">implements</span><span class="pln"> </span><a href="api/core/OnInit" class="code-anchor"><span class="typ">OnInit</span></a><span class="pln"> </span><span class="pun">{</span><span class="pln">

  selectedHero</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">;</span><span class="pln">

  heroes</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">[];</span><span class="pln">

  </span><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">private</span><span class="pln"> heroService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">HeroService</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">private</span><span class="pln"> messageService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span><span class="pln">

  ngOnInit</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">getHeroes</span><span class="pun">();</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

  onSelect</span><span class="pun">(</span><span class="pln">hero</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">):</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">selectedHero </span><span class="pun">=</span><span class="pln"> hero</span><span class="pun">;</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messageService</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">`HeroService: Selected hero id=${hero.id}`</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">

  getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroService</span><span class="pun">.</span><span class="pln">getHeroes</span><span class="pun">()</span><span class="pln">
        </span><span class="pun">.</span><span class="pln">subscribe</span><span class="pun">(</span><span class="pln">heroes </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">heroes </span><span class="pun">=</span><span class="pln"> heroes</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">刷新浏览器，页面显示出了英雄列表。 滚动到底部，就会在消息区看到来自 <code>HeroService</code> 的消息。 点击“清空”按钮，消息区不见了。</p><p translation-origin="off">The browser refreshes and the page displays the list of heroes. Refresh the browser to see the list of heroes, and scroll to the bottom to see the messages from the HeroService. Each time you click a hero, a new message appears to record the selection. Use the "clear" button to clear the message history.</p><a id="final-code-review"></a><h2 id="final-code-review" translation-result="on">查看最终代码<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#final-code-review"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="final-code-review">Final code review<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#final-code-review"><i class="material-icons">link</i></a></h2><p translation-result="on">你的应用应该变成了这样<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="在线例子" href="generated/live-examples/toh-pt4/stackblitz.html">在线例子</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/toh-pt4/toh-pt4.zip">下载范例</a></span></span></span></live-example>。本页所提及的代码文件如下：</p><p translation-origin="off">Here are the code files discussed on this page and your app should look like this<live-example ng-version="9.0.0-rc.11"><span style="display:none"></span><span><span class="ng-star-inserted"><a target="_blank" title="在线例子" href="generated/live-examples/toh-pt4/stackblitz.html">在线例子</a><span class="ng-star-inserted"> / <a download="" title="下载范例" href="generated/zips/toh-pt4/toh-pt4.zip">下载范例</a></span></span></span></live-example>.</p><code-tabs ng-version="9.0.0-rc.11"><div style="display:none"><code-pane header="src/app/hero.service.ts" path="toh-pt4/src/app/hero.service.ts">import { <a href="api/core/Injectable" class="code-anchor">Injectable</a> } from '@angular/core'; import { Observable, of } from 'rxjs'; import { Hero } from './hero'; import { HEROES } from './mock-heroes'; import { MessageService } from './message.service'; @<a href="api/core/Injectable" class="code-anchor">Injectable</a>({ <a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root', }) export class HeroService { constructor(private messageService: MessageService) { } getHeroes(): Observable&lt;Hero[]&gt; { // TODO: send the <a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a> _after_ fetching the heroes this.messageService.add('HeroService: fetched heroes'); return of(HEROES); } }</code-pane><code-pane header="src/app/message.service.ts" path="toh-pt4/src/app/message.service.ts">import { <a href="api/core/Injectable" class="code-anchor">Injectable</a> } from '@angular/core'; @<a href="api/core/Injectable" class="code-anchor">Injectable</a>({ <a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>: 'root', }) export class MessageService { <a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a>: string[] = []; add(<a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>: string) { this.messages.push(<a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>); } clear() { this.messages = []; } }</code-pane><code-pane header="src/app/heroes/heroes.component.ts" path="toh-pt4/src/app/heroes/heroes.component.ts">import { <a href="api/core/Component" class="code-anchor">Component</a>, <a href="api/core/OnInit" class="code-anchor">OnInit</a> } from '@angular/core'; import { Hero } from '../hero'; import { HeroService } from '../hero.service'; import { MessageService } from '../message.service'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-heroes', <a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a>: './heroes.component.html', <a href="api/core/Component#styleUrls" class="code-anchor">styleUrls</a>: ['./heroes.component.css'] }) export class HeroesComponent implements <a href="api/core/OnInit" class="code-anchor">OnInit</a> { selectedHero: Hero; heroes: Hero[]; constructor(private heroService: HeroService, private messageService: MessageService) { } ngOnInit() { this.getHeroes(); } onSelect(hero: Hero): void { this.selectedHero = hero; this.messageService.add(`HeroService: Selected hero id=${hero.id}`); } getHeroes(): void { this.heroService.getHeroes() .subscribe(heroes =&gt; this.heroes = heroes); } }</code-pane><code-pane header="src/app/messages/messages.component.ts" path="toh-pt4/src/app/messages/messages.component.ts">import { <a href="api/core/Component" class="code-anchor">Component</a>, <a href="api/core/OnInit" class="code-anchor">OnInit</a> } from '@angular/core'; import { MessageService } from '../message.service'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-messages', <a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a>: './messages.component.html', <a href="api/core/Component#styleUrls" class="code-anchor">styleUrls</a>: ['./messages.component.css'] }) export class MessagesComponent implements <a href="api/core/OnInit" class="code-anchor">OnInit</a> { constructor(public messageService: MessageService) {} ngOnInit() { } }</code-pane><code-pane header="src/app/messages/messages.component.html" path="toh-pt4/src/app/messages/messages.component.html">&lt;div *<a href="api/common/NgIf" class="code-anchor">ngIf</a>="messageService.messages.length"&gt; &lt;h2&gt;Messages&lt;/h2&gt; &lt;button class="clear" (click)="messageService.clear()"&gt;clear&lt;/button&gt; &lt;div *<a href="api/common/NgForOf" class="code-anchor">ngFor</a>='let <a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a> of messageService.messages'&gt; {{<a href="api/common/http/HttpErrorResponse#message" class="code-anchor">message</a>}} &lt;/div&gt; &lt;/div&gt;</code-pane><code-pane header="src/app/messages/messages.component.css" path="toh-pt4/src/app/messages/messages.component.css">/* MessagesComponent's private CSS styles */ h2 { color: red; font-family: Arial, Helvetica, sans-serif; font-weight: lighter; } body { margin: 2em; } body, input[text], button { color: crimson; font-family: Cambria, Georgia; } button.clear { font-family: Arial; background-color: #eee; border: none; padding: 5px 10px; border-radius: 4px; cursor: pointer; cursor: hand; } button:hover { background-color: #cfd8dc; } button:disabled { background-color: #eee; color: #aaa; cursor: auto; } button.clear { color: #333; margin-bottom: 12px; }</code-pane><code-pane header="src/app/app.module.ts" path="toh-pt4/src/app/app.module.ts">import { <a href="api/platform-browser/BrowserModule" class="code-anchor">BrowserModule</a> } from '@angular/platform-browser'; import { <a href="api/core/NgModule" class="code-anchor">NgModule</a> } from '@angular/core'; import { <a href="api/forms/FormsModule" class="code-anchor">FormsModule</a> } from '@angular/forms'; import { AppComponent } from './app.component'; import { HeroesComponent } from './heroes/heroes.component'; import { HeroDetailComponent } from './hero-detail/hero-detail.component'; import { MessagesComponent } from './<a href="api/service-worker/SwPush#messages" class="code-anchor">messages</a>/messages.component'; @<a href="api/core/NgModule" class="code-anchor">NgModule</a>({ declarations: [ AppComponent, HeroesComponent, HeroDetailComponent, MessagesComponent ], imports: [ <a href="api/platform-browser/BrowserModule" class="code-anchor">BrowserModule</a>, <a href="api/forms/FormsModule" class="code-anchor">FormsModule</a> ], providers: [ // no need to place any providers due to the `<a href="api/core/Injectable#providedIn" class="code-anchor">providedIn</a>` flag... ], bootstrap: [ AppComponent ] }) export class AppModule { }</code-pane><code-pane header="src/app/app.component.html" path="toh-pt4/src/app/app.component.html">&lt;h1&gt;{{title}}&lt;/h1&gt; &lt;app-heroes&gt;&lt;/app-heroes&gt; &lt;app-messages&gt;&lt;/app-messages&gt;</code-pane></div><mat-card class="mat-card"><mat-tab-group class="mat-tab-group code-tab-group mat-primary"><mat-tab-header class="mat-tab-header mat-tab-header-pagination-controls-enabled"><div aria-hidden="true" mat-ripple="" class="mat-ripple mat-tab-header-pagination mat-tab-header-pagination-before mat-elevation-z4 mat-tab-header-pagination-disabled"><div class="mat-tab-header-pagination-chevron"></div></div><div class="mat-tab-label-container"><div role="tablist" class="mat-tab-list" style="transform:translateX(0)"><div class="mat-tab-labels"><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label mat-tab-label-active ng-star-inserted" id="mat-tab-label-1-0" tabindex="0" aria-posinset="1" aria-setsize="8" aria-controls="mat-tab-content-1-0" aria-selected="true" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/hero.service.ts</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-1" tabindex="-1" aria-posinset="2" aria-setsize="8" aria-controls="mat-tab-content-1-1" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/message.service.ts</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-2" tabindex="-1" aria-posinset="3" aria-setsize="8" aria-controls="mat-tab-content-1-2" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/heroes/heroes.component.ts</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-3" tabindex="-1" aria-posinset="4" aria-setsize="8" aria-controls="mat-tab-content-1-3" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/messages/messages.component.ts</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-4" tabindex="-1" aria-posinset="5" aria-setsize="8" aria-controls="mat-tab-content-1-4" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/messages/messages.component.html</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-5" tabindex="-1" aria-posinset="6" aria-setsize="8" aria-controls="mat-tab-content-1-5" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/messages/messages.component.css</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-6" tabindex="-1" aria-posinset="7" aria-setsize="8" aria-controls="mat-tab-content-1-6" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/app.module.ts</span></div></div><div role="tab" mattablabelwrapper="" mat-ripple="" cdkmonitorelementfocus="" class="mat-ripple mat-tab-label ng-star-inserted" id="mat-tab-label-1-7" tabindex="-1" aria-posinset="8" aria-setsize="8" aria-controls="mat-tab-content-1-7" aria-selected="false" aria-disabled="false"><div class="mat-tab-label-content"><span class="ng-star-inserted">src/app/app.component.html</span></div></div></div><mat-ink-bar class="mat-ink-bar" style="visibility:visible;left:0;width:189px"></mat-ink-bar></div></div><div aria-hidden="true" mat-ripple="" class="mat-ripple mat-tab-header-pagination mat-tab-header-pagination-after mat-elevation-z4"><div class="mat-tab-header-pagination-chevron"></div></div></mat-tab-header><div class="mat-tab-body-wrapper"><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-4 mat-tab-body-active ng-star-inserted" id="mat-tab-content-1-0" aria-labelledby="mat-tab-label-1-0"><div class="mat-tab-body-content ng-tns-c50-4 ng-trigger ng-trigger-translateTab" style="transform:none"><aio-code class="ng-star-inserted" style=""><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="Copy code snippet from src/app/hero.service.ts">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><a href="api/core/Injectable" class="code-anchor"><span class="typ">Injectable</span></a><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'@angular/core'</span><span class="pun">;</span><span class="pln">

</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Observable</span><span class="pun">,</span><span class="pln"> of </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'rxjs'</span><span class="pun">;</span><span class="pln">

</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">Hero</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./hero'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> HEROES </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./mock-heroes'</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">import</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">from</span><span class="pln"> </span><span class="str">'./message.service'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Injectable" class="code-anchor"><span class="lit">Injectable</span></a><span class="pun">({</span><span class="pln">
  </span><a href="api/core/Injectable#providedIn" class="code-anchor"><span class="pln">providedIn</span></a><span class="pun">:</span><span class="pln"> </span><span class="str">'root'</span><span class="pun">,</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroService</span><span class="pln"> </span><span class="pun">{</span><span class="pln">

  </span><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">private</span><span class="pln"> messageService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">MessageService</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">}</span><span class="pln">

  getHeroes</span><span class="pun">():</span><span class="pln"> </span><span class="typ">Observable</span><span class="pun">&lt;</span><span class="typ">Hero</span><span class="pun">[]&gt;</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="com">// TODO: send the </span><a href="api/common/http/HttpErrorResponse#message" class="code-anchor"><span class="com">message</span></a><span class="com"> _after_ fetching the heroes</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">messageService</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="str">'HeroService: fetched heroes'</span><span class="pun">);</span><span class="pln">
    </span><span class="kwd">return</span><span class="pln"> of</span><span class="pun">(</span><span class="pln">HEROES</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-5 ng-star-inserted" id="mat-tab-content-1-1" aria-labelledby="mat-tab-label-1-1"><div class="mat-tab-body-content ng-tns-c50-5 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-6 ng-star-inserted" id="mat-tab-content-1-2" aria-labelledby="mat-tab-label-1-2"><div class="mat-tab-body-content ng-tns-c50-6 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-7 ng-star-inserted" id="mat-tab-content-1-3" aria-labelledby="mat-tab-label-1-3"><div class="mat-tab-body-content ng-tns-c50-7 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-8 ng-star-inserted" id="mat-tab-content-1-4" aria-labelledby="mat-tab-label-1-4"><div class="mat-tab-body-content ng-tns-c50-8 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-9 ng-star-inserted" id="mat-tab-content-1-5" aria-labelledby="mat-tab-label-1-5"><div class="mat-tab-body-content ng-tns-c50-9 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-10 ng-star-inserted" id="mat-tab-content-1-6" aria-labelledby="mat-tab-label-1-6"><div class="mat-tab-body-content ng-tns-c50-10 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body><mat-tab-body role="tabpanel" class="mat-tab-body ng-tns-c50-11 ng-star-inserted" id="mat-tab-content-1-7" aria-labelledby="mat-tab-label-1-7"><div class="mat-tab-body-content ng-tns-c50-11 ng-trigger ng-trigger-translateTab" style="transform:translate3d(100%,0,0);min-height:1px"></div></mat-tab-body></div></mat-tab-group></mat-card></code-tabs><h2 id="summary" translation-result="on">小结<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#summary"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="summary">Summary<a title="Link to this heading" class="header-link" aria-hidden="true" href="tutorial/toh-pt4#summary"><i class="material-icons">link</i></a></h2><ul><li><p translation-result="on">你把数据访问逻辑重构到了 <code>HeroService</code> 类中。</p><p translation-origin="off">You refactored data access to the <code>HeroService</code> class.</p></li><li><p translation-result="on">你在根注入器中把 <code>HeroService</code> 注册为该服务的提供商，以便在别处可以注入它。</p><p translation-origin="off">You registered the <code>HeroService</code> as the <em>provider</em> of its service at the root level so that it can be injected anywhere in the app.</p></li><li><p translation-result="on">你使用 <a href="guide/dependency-injection">Angular 依赖注入</a>机制把它注入到了组件中。</p><p translation-origin="off">You used <a href="guide/dependency-injection">Angular Dependency Injection</a> to inject it into a component.</p></li><li><p translation-result="on">你给 <code>HeroService</code> 中获取数据的方法提供了一个异步的函数签名。</p><p translation-origin="off">You gave the <code>HeroService</code> <em>get data</em> method an asynchronous signature.</p></li><li><p translation-result="on">你发现了 <code>Observable</code> 以及 RxJS 库。</p><p translation-origin="off">You discovered <code>Observable</code> and the RxJS <em>Observable</em> library.</p></li><li><p translation-result="on">你使用 RxJS 的 <code>of()</code> 方法返回了一个模拟英雄数据的<em>可观察对象</em> (<code>Observable&lt;Hero[]&gt;</code>)。</p><p translation-origin="off">You used RxJS <code>of()</code> to return an observable of mock heroes (<code>Observable&lt;Hero[]&gt;</code>).</p></li><li><p translation-result="on">在组件的 <code>ngOnInit</code> 生命周期钩子中调用 <code>HeroService</code> 方法，而不是构造函数中。</p><p translation-origin="off">The component's <code>ngOnInit</code> lifecycle hook calls the <code>HeroService</code> method, not the constructor.</p></li><li><p translation-result="on">你创建了一个 <code>MessageService</code>，以便在类之间实现松耦合通讯。</p><p translation-origin="off">You created a <code>MessageService</code> for loosely-coupled communication between classes.</p></li><li><p translation-result="on"> <code>HeroService</code> 连同注入到它的服务 <code>MessageService</code> 一起，注入到了组件中。</p><p translation-origin="off">The <code>HeroService</code> injected into a component is created with another injected service, <code>MessageService</code>.</p></li></ul></div></div></aio-doc-viewer></main></mat-sidenav-content></mat-sidenav-container><div class="toc-container no-print ng-star-inserted"><aio-lazy-ce selector="aio-toc"><aio-toc ng-version="9.0.0-rc.11"><div class="toc-inner no-print collapsed ng-star-inserted"><ul class="toc-list"><li class="h1 ng-star-inserted active" title="服务"><a href="tutorial/toh-pt4#create-services">服务</a></li><li class="h2 ng-star-inserted" title="为什么需要服务"><a href="tutorial/toh-pt4#why-services">为什么需要服务</a></li><li class="h2 ng-star-inserted" title="创建 HeroService"><a href="tutorial/toh-pt4#create-the-heroservice">创建 <code>HeroService</code></a></li><li class="h3 ng-star-inserted" title="@Injectable() 服务"><a href="tutorial/toh-pt4#injectable-services"><code>@Injectable()</code> 服务</a></li><li class="h3 ng-star-inserted" title="获取英雄数据"><a href="tutorial/toh-pt4#get-hero-data">获取英雄数据</a></li><li class="h2 ng-star-inserted" title="提供（provide） HeroService"><a href="tutorial/toh-pt4#provide-the-heroservice">提供（provide） <code>HeroService</code></a></li><li class="h2 ng-star-inserted" title="修改 HeroesComponent"><a href="tutorial/toh-pt4#update-heroescomponent">修改 <code>HeroesComponent</code></a></li><li class="h3 ng-star-inserted" title="注入 HeroService"><a href="tutorial/toh-pt4#inject-the-heroservice">注入 <code>HeroService</code></a></li><li class="h3 ng-star-inserted" title="添加 getHeroes()"><a href="tutorial/toh-pt4#add-getheroes">添加 <em>getHeroes()</em></a></li><li class="h3 ng-star-inserted" title="在 ngOnInit() 中调用它"><a href="tutorial/toh-pt4#call-it-in-ngoninit">在 <code>ngOnInit()</code> 中调用它</a></li><li class="h3 ng-star-inserted" title="查看运行效果"><a href="tutorial/toh-pt4#see-it-run">查看运行效果</a></li><li class="h2 ng-star-inserted" title="可观察（Observable）的数据"><a href="tutorial/toh-pt4#observable-data">可观察（Observable）的数据</a></li><li class="h3 ng-star-inserted" title="可观察对象版本的 HeroService"><a href="tutorial/toh-pt4#observable-heroservice">可观察对象版本的 <code>HeroService</code></a></li><li class="h3 ng-star-inserted" title="在 HeroesComponent 中订阅"><a href="tutorial/toh-pt4#subscribe-in-heroescomponent">在 <code>HeroesComponent</code> 中订阅</a></li><li class="h2 ng-star-inserted" title="显示消息"><a href="tutorial/toh-pt4#show-messages">显示消息</a></li><li class="h3 ng-star-inserted" title="创建 MessagesComponent"><a href="tutorial/toh-pt4#create-messagescomponent">创建 <code>MessagesComponent</code></a></li><li class="h3 ng-star-inserted" title="创建 MessageService"><a href="tutorial/toh-pt4#create-the-messageservice">创建 <code>MessageService</code></a></li><li class="h3 ng-star-inserted" title="把它注入到 HeroService 中"><a href="tutorial/toh-pt4#inject-it-into-the-heroservice">把它注入到 <code>HeroService</code> 中</a></li><li class="h3 ng-star-inserted" title="从 HeroService 中发送一条消息"><a href="tutorial/toh-pt4#send-a-message-from-heroservice">从 <code>HeroService</code> 中发送一条消息</a></li><li class="h3 ng-star-inserted" title="从 HeroService 中显示消息"><a href="tutorial/toh-pt4#display-the-message-from-heroservice">从 <code>HeroService</code> 中显示消息</a></li><li class="h3 ng-star-inserted" title="绑定到 MessageService"><a href="tutorial/toh-pt4#bind-to-the-messageservice">绑定到 <code>MessageService</code></a></li><li class="h2 ng-star-inserted" title="为 hero 服务添加额外的消息"><a href="tutorial/toh-pt4#add-additional-messages-to-hero-service">为 hero 服务添加额外的消息</a></li><li class="h2 ng-star-inserted" title="查看最终代码"><a href="tutorial/toh-pt4#final-code-review">查看最终代码</a></li><li class="h2 ng-star-inserted" title="小结"><a href="tutorial/toh-pt4#summary">小结</a></li></ul></div></aio-toc></aio-lazy-ce></div><footer class="no-print"><aio-footer><div class="grid-fluid"><div class="footer-block ng-star-inserted"><h3>资源</h3><ul><li class="ng-star-inserted"><a class="link" href="about" title="Angular 贡献者。">关于</a></li><li class="ng-star-inserted"><a class="link" href="resources" title="网络上的 Angular 工具、培训、博客等">资源列表</a></li><li class="ng-star-inserted"><a class="link" href="presskit" title="我们的联系方式、LOGO 和品牌">宣传资料</a></li><li class="ng-star-inserted"><a class="link" href="https://blog.angular.io/" title="Angular 官方博客">博客</a></li><li class="ng-star-inserted"><a class="link" href="analytics" title="Angular 使用情况分析">使用情况分析</a></li></ul></div><div class="footer-block 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